1. Field of Invention
The present invention relates to ink for an ink-jet printer containing a fluorescent compound which has no absorption in the visible light range, and which emits fluorescence by ultraviolet irradiation. The invention also relates to ink for ink-jet printer containing a fluorescent compound which has absorption in the visible light range, and which emits fluorescence by ultraviolet irradiation.
2. Description of Related Art
Ink-jet printing is performed in such a way that letters, graphics, and images are directly printed on recording media by ejecting ink from a fine nozzle as droplets. A drop-on-demand system and a continuous system are exemplary systems of ink-jet printing.
The drop-on-demand system is a system in which ink is ejected as needed, and ink-jet printers of this system have been used as printers for personal computers, etc. The continuous system is a system in which continuously ejected ink particles are charged in accordance with electric signals, and only needed ink particles are ejected on paper. The continuous system is superior in high-speed printing.
In common ink for an ink-jet printer, a coloring agent, which absorbs a part of visible light and generates reflected light (which has reflected light) under visible light, is contained at a concentration at which the color of print is visible to the naked eye. On the other hand, fluorescent ink containing a fluorescent compound, which has no absorption in the visible light range and which emits fluorescence (emits light in the visible light range) by ultraviolet irradiation, is disclosed in Japanese Unexamined Patent Application Publication No. 58-49765 and Japanese Unexamined Patent Application Publication No. 11-152436.
In Japanese Unexamined Patent Application Publication No. 58-49765, an ink for ink-jet printer containing a fluorescent compound, which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation at a concentration at which a recording concentration on recording paper becomes 0.1 or less on an optical density basis (that is, a content at which the color of print is not visible to the naked eye under visible light), is disclosed.
When each of the ink described in these publications and common ink for ink-jet printer are respectively ejected from a plurality of nozzles of an ink-jet head, for example, letters that are to be shown to a person, and letters which emit fluorescence by ultraviolet irradiation, can be printed at the same time with ease. That is, the print part is visually identified under the visible light, for example, sunlight, fluorescent light, and incandescent lamp, and under the light source having a predetermined spectral energy distribution with different hue, lightness, and chroma.
However, since the florescent ink disclosed in Japanese Unexamined Patent Application Publication No. 11-152436 is for an ink-jet printer of the continuous system, when this ink is used for an ink-jet printer of the drop-on-demand system, printing reliability may be reduced because of a difference in the print system.
Herein, the fluorescent ink used for the ink-jet printer, in which the printing system is the drop-on-demand system, is required to have the following characteristics.
(1) High quality images are produced on plain paper.
(2) The ink is promptly fixed and, therefore, high-speed printing can be performed.
(3) Nozzles are not clogged, and stable ejection can be performed, wherein skew in ejection (this refers to that the ink is not ejected in the precisely downward direction, but is ejected in the slanting direction) and dot dropout do not occur.
(4) The hue, lightness, and chroma of the print part are significantly changed by irradiation of light source.
In the related art, in order to address (2) above, many sorts of ink have been suggested, wherein an organic solvent or surfactant (referred to as xe2x80x9cpenetrantxe2x80x9d) is added in the ink. Among them, in the related art, when an acetylene glycol (acetylenediol)-based surfactant is used, prints with no blur can be produced by deep permeation of the ink in the direction of the thickness of paper, while the printing speed is ensured. Japanese Unexamined Patent Application Publication No. 4-359071 discloses this feature.
In order to address (4) above, significantly changing the hue of the print part, the ink containing a plurality of fluorescent compounds which are substantially transparent with respect to visible light, and which emit fluorescence by irradiation of ultraviolet lights having different wavelengths has been known. Japanese Unexamined Patent Application Publication No. 10-251570 discloses this feature. However, in this method, a specific apparatus capable of irradiating a plurality of ultraviolet lights is required for the detection.
In order to address (4) above, significantly changing the lightness and chroma of the print part, for example, an ink composition using transparent fine solid particles having a particle diameter of 1 xcexcm or less is disclosed in Japanese Unexamined Patent Application Publication No. 9-78022. This publication discloses that when fine particles are added, the fine particles are fixed on the surface of the paper, a fluorescent dye is adsorbed thereon and, therefore, the concentration of the fluorescent dye is increased, and the emission intensity during ultraviolet irradiation is increased. Consequently, it is believed that in this case, when the acetylenediol-based surfactant is used for the purpose of (2) above, the fluorescent compound in the fluorescent ink deeply permeates into the paper and, therefore, adequate fluorescence emission intensity is not achieved.
As described above, regarding the ink containing the fluorescent compound for an ink-jet printer of the drop-on-demand system, products capable of satisfying all points of quick-drying property of the ink after printing, print quality, and change in the hue, lightness, and chroma of the print part by irradiation of light source have been required, and, therefore, the ink disclosed in each of the aforementioned publications is susceptible to further enhancement.
Accordingly, it is a first object of the present invention to provide an ink for an ink-jet printer containing a fluorescent compound which has no absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, a surfactant, and water, such that the ink can satisfy all points of quick-drying property of the ink after printing, print quality, and change in the hue, lightness, and chroma of the print part by irradiation of light source.
It is a second object of the present invention to provide an ink for an ink-jet printer containing a fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, a surfactant, and water, such that the ink can satisfy all points of quick-drying property of the ink after printing, print quality, and change in the hue, lightness, and saturation of the print part by irradiation of light source.
In order to address the aforementioned problems, the present invention provides an ink for an ink-jet printer containing a fluorescent compound which has no absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, a surfactant, and water. The ink for an ink-jet printer is provided such in that the surfactant is an acetylenediol (acetylene glycol)-based surfactant represented by the following Chemical formula (1) and formed of a mixture of a first compound and a second compound where R is an isobutyl group (xe2x80x94CH2CH(CH3)CH3) and where R is an ethyl group (xe2x80x94CH2CH3), respectively, and where when the content of the first compound in the ink is indicated by A (% by weight) and the content of the second compound is indicated by B (% by weight), A and B are more than xe2x80x9c0xe2x80x9d, and the relationship between A and B is configured to satisfy the following mathematical expression 5.0xe2x89xa616A+Bxe2x89xa66.5. This is referred to as xe2x80x9cthe first inkxe2x80x9d of the present invention. 
The present invention provides an ink for an ink-jet printer containing a fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, a surfactant, and water. The ink for an ink-jet printer is provided such that the surfactant is an acetylenediol (acetylene glycol)-based surfactant represented by the aforementioned Chemical formula (1) and is formed of a mixture of a first compound and a second compound where R is an isobutyl group (xe2x80x94CH2CH(CH3)CH3) and where R is an ethyl group (xe2x80x94CH2CH3), respectively, and that where the content of the first compound in the ink is indicated by A (% by weight) and the content of the second compound is indicated by B (% by weight), A and B are more than xe2x80x9c0xe2x80x9d, and the relationship between A and B is configured to satisfy the aforementioned mathematical expression (1). This is referred to as xe2x80x9cthe second inkxe2x80x9d of the present invention.
The surface tension of the first compound is 26 to 38 mN/m, and the surface tension of the second compound is 50 mN/m or more.
The present invention provides an ink for an ink-jet printer that is formed of a fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation and a fluorescent compound which has no absorption in the visible light range and which emits fluorescence, by ultraviolet irradiation, with a hue different from the hue of the fluorescence emitted from the aforementioned fluorescent compound under visible light. This is referred to as xe2x80x9cthe third inkxe2x80x9d of the present invention.
According to the first ink and the second ink of the present invention, by using the surfactant mixed in order that the relationship between the contents A and B of the first compound and the second compound in the ink may satisfy the aforementioned mathematical expression (1), the ink capable of satisfying all points of quick-drying property of the ink after printing, print quality, and change in the hue, lightness, and chroma of the print part by irradiation of light source can be produced as an ink for an ink-jet printer containing a fluorescent compound, a surfactant, and water.
Regarding the first ink and the second ink of the present invention, where xe2x80x9c16A+Bxe2x80x9d is less than 5.0, an effect of enhancing permeability of the ink is not sufficient, and where it exceeds 6.5, blurring occurs, an ejecting condition of the ink is adversely affected and, therefore, the print quality is degraded.
As the first compound constituting the surfactant used for the first ink and the second ink of the present invention, xe2x80x9cSurfynol 104xe2x80x9d manufactured by Air Products and Chemicals. Inc., is commercially available. As the second compound, xe2x80x9cSurfynol 82xe2x80x9d manufactured by Air Products and Chemicals. Inc., is commercially available.
The contents of the surfactants in the first ink and the second ink of the present invention are preferably within the range of not less than 0.3% by weight to not more than 5.0% by weight relative to the total amount of the ink.
In the first ink of the present invention, as the fluorescent compound, dies referred to as xe2x80x9cfluorescent whitenerxe2x80x9d can be used. For example, diaminostilbene-based, distyrylbiphenyl-based, imidazole-based, naphthalimide-based, and coumalin-based fluorescent whiteners, etc., can be used. Examples of commercially available products include, for example, xe2x80x9cKayaphor AP Liquidxe2x80x9d, xe2x80x9cKayaphor GMY Liquidxe2x80x9d, and xe2x80x9cKayaphor S Liquidxe2x80x9d manufactured by NIPPON KAYAKU COLORS CO., LTD., xe2x80x9cTINOPAL ABP-Z Liquidxe2x80x9d, xe2x80x9cTINOPAL MSP Liquidxe2x80x9d, xe2x80x9cUVITEX NFW Liquidxe2x80x9d, and xe2x80x9cTINOPAL UP Liquidxe2x80x9d manufactured by Ciba Specialty Chemicals.
In the second ink of the present invention, as the fluorescent compound, dies referred to as xe2x80x9cfluorescent dyexe2x80x9d, pigments referred to as xe2x80x9cfine particle fluorescent pigmentxe2x80x9d, in which fine particles made of a synthetic resin are dyed with a fluorescent dye, can be used. Examples of commercially available products include, for example, xe2x80x9cKayanol Rhodamine FBxe2x80x9d, xe2x80x9cKayafect Yellow G Liqxe2x80x9d, xe2x80x9cKayafect Yellow C Liqxe2x80x9d, xe2x80x9cKayarus Light Yellow F8Gxe2x80x9d, xe2x80x9cKayanol Brilliant Flavine FLxe2x80x9d, xe2x80x9cKayaset Flavine F2Gxe2x80x9d, xe2x80x9cKayacryl Brill.Pnik B-EDxe2x80x9d, and xe2x80x9cKayacryl Brill.Pink B200xe2x80x9d manufactured by NIPPON KAYAKU COLORS CO., LTD. Examples of fluorescent pigments include, for example, xe2x80x9cLUMIKOL NKW-3002xe2x80x9d, xe2x80x9cLUMIKOL NKW-3003xe2x80x9d, xe2x80x9cLUMIKOL NKW-3004xe2x80x9d, xe2x80x9cLUMIKOL NKW-3005xe2x80x9d, and xe2x80x9cLUMIKOL NKW-3007xe2x80x9d, which have an average particle diameter of about 100 nm, manufactured by Nippon Keiko Kagaku K.K., xe2x80x9cSF-5012xe2x80x9d, xe2x80x9cSF-5013xe2x80x9d, xe2x80x9cSF-5014xe2x80x9d, xe2x80x9cSF-5015xe2x80x9d, xe2x80x9cSF-5017xe2x80x9d, and xe2x80x9cSF-5037xe2x80x9d, which have an average particle diameter of about 100 nm, manufactured by SINLOIHI CO., LTD., and xe2x80x9cSF-7012xe2x80x9d, xe2x80x9cSF-7014xe2x80x9d, xe2x80x9cSF-7015xe2x80x9d, and xe2x80x9cSF-7017xe2x80x9d, which have an average particle diameter of about 400 nm, manufactured by SINLOIHI CO., LTD.
When the ink of the present invention is applied to printing using an ink-jet recording apparatus, it is desirable to use a fluorescent dye having excellent printing reliability and ink preservation stability as the fluorescent compound. For example, where dispersing elements dispersed in water are used, the average particle diameter of the aforementioned dispersing elements is desirably 500 nm or less, and more desirably, is 300 nm or less. By making the particle diameter of the dispersing elements fine, ink dispersion stability, nozzle clogging property in the ink-jet recording apparatus, etc., can be enhanced.
Regarding conventional ink compositions, where the content of the fluorescent compound is high, concentration quenching occurs, fluorescent emission intensity is reduced significantly and, therefore, sometimes practically adequate fluorescent emission intensity cannot be achieved. On the other hand, regarding the ink composition of the first or second ink of the present invention, by specifying the surfactants as described above, the fluorescent compound in the ejected ink permeates into not only the surface, but also the inside of the paper and is distributed over a wide range. Accordingly, even where the content of the fluorescent compound is a high concentration compared to a conventional value, significant reduction of the fluorescent emission intensity due to the concentration quenching does not occur.
According to the third ink of the present invention, by mixing and using the fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation and the fluorescent compound which has no absorption in the visible light range and which emits fluorescence, by ultraviolet irradiation, with a hue different from that of the fluorescence emitted from the aforementioned fluorescent compound under visible light, an ink, in which the hue, lightness, and chroma of the print part significantly change by ultraviolet irradiation, can be produced.
Regarding the ink of the present invention, although the content of the aforementioned fluorescent compound in the ink is appropriately determined in accordance with the required characteristics, it is preferably 0.1% by weight or more, but 20% by weight or less, and more preferably, is 1.0% by weight or more, but 15% by weight or less. Where the addition amount is more than 20% by weight, clogging at the nozzle tip becomes likely to occur in spite of the addition of a humectant, and the printing reliability is reduced. Where the content of the fluorescent compound is less than 0.1% by weight, the change in the hue, lightness, and chroma of the print part is small in the case where ultraviolet irradiation is performed and, therefore, visibility is poor.
For example, in the case where contents of a print are desired to be made invisible under visible light, it is necessary to use a fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, and to make the content thereof usually 1.0% by weight or less although depending on the coloring power of the fluorescent compound. In this case, it is desirable to use a fluorescent compound providing Yellow reflected color having a low relative luminous efficiency as the fluorescent compound.
Where the hue, lightness, and chroma of the print part is changed by irradiation of light source, while the visibility of the print is ensured, in order to prevent print forgery by, for example, color copy, etc., it is necessary to use a fluorescent compound which has absorption in the visible light range and which emits fluorescence by ultraviolet irradiation, and to make the content thereof usually 1.0% by weight or more although depending on the coloring power of the fluorescent compound.
The ink of the present invention preferably contains polyhydric alcohols in order to prevent clogging of nozzles. Specific examples of polyhydric alcohols include, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol having a molecular weight of 2,000 or less, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin, thioglycol, mesoerythritol, pentaerythritol.
Among these, glycerin, 1,5-pentanediol, diethylene glycol, and furthermore, mixtures thereof are preferable because the viscosity of the ink composition can be properly controlled, and clogging of nozzles can be prevented effectively. The addition amounts of these polyhydric alcohols are preferably 3% to less than 40% by weight relative to the ink composition, and more preferably, are 5% to 30% by weight.